Evidence that endothelin-1 (ET-1) inhibits insulin-stimulated glucose uptake in rat adipocytes mainly through ETA receptors

Abstract The specificity of endothelin (ET) receptors involved in the inhibition of insulin-stimulated glucose uptake (ISGU) in rat adipocytes was investigated. Adipocytes were isolated from the epididymal fat pads of Sprague-Dawley rats. To determine receptor subtypes, we used three ET isopeptides, ET-1 and ET-2, both of which are nonselective agonists, and ET-3, a selective agonist for ET c receptors, to displace [ 125 I]ET-1 binding from the fat cells. The efficiency of displacement was ET-1 > ET-2 ⪢ ET-3, indicating that the primary receptors involved belonged to the ET a subtype. At an equal concentration of 1 μmol/L, BQ-610, a selective ET a antagonist, displaced [ 125 I]ET-1 from binding to fat cells, whereas IRL-1038, a selective ET b antagonist, did not. Using [ 3 H]2-deoxy- d -1-glucose ([ 3 H]2-DG) as a tracer in studies of glucose uptake, we found that equimolar BQ-610 completely reversed the inhibitory effect of ET-1 on ISGU, whereas IRL-1038 was ineffective. Northern blot analysis of adipocyte receptors showed abundant mRNA for ET a , but no ET b subtype. These results clearly demonstrate that ET a is the predominant receptor in rat adipocytes.